LED backlight chips with a boost converter often utilize a power-line FET (field effect transistor) to switch off the current from the supply when the chip is off. It is also necessary to protect against high current conditions created by a short circuit at the output. The power-line FET can be used to limit the current flow during the initial in-rush period and also to protect against output short circuit fault conditions.
Various short circuit detection methods are commonly used which utilize either a sense resistor or a replica device. These methods require additional components and also add to the system power loss. It is also possible to use a component already existing in the current flow path and use its impedance to measure current and detect an over-current condition. Because of the variation of the sensing element's impedance from one component to the next, these methods usually lack accuracy.
As such, it is desirable to have a method to improve the accuracy of short circuit detection in LED backlight chips using the resistance of a component already existing in the current flow path to detect an over-current condition.